Luminescent properties of phosphor converted LED using an orange-emitting Rb ₂CaP ₂O ₇:Eu ²⁺ phosphor

A series of orange-emitting Rb ₂CaP ₂O ₇:Eu ²⁺ phosphors were synthesized by a conventional solid-state reaction method. The as-prepared phosphors were characterized by X-ray powder diffraction (XRD), fluorescence spectroscopy, and spectroradiometry. XRD showed that all prepared samples exhibited a monoclinic Rb ₂CaP ₂O ₇ phase. Fluorescence spectroscopy showed that the photoluminescence efficiency of Rb ₂Ca _1-xP ₂O ₇:Eu _x ²⁺ phosphors increased with increasing Eu ²⁺ concentration until x = 0.006, then decreased at higher concentrations, due to a concentration quenching effect. The thermal activation energy was also measured to be 0.40 eV. Furthermore, a phosphor-converted LED (pc-LED) coated with Rb ₂Ca _0.994P ₂O ₇:Eu _0.006 ²⁺ was fabricated, which exhibited bright orange emission under a forward bias, from 200 to 300 mA. The color rendering index (CRI) of pc-LED coated with Rb ₂Ca _0.994P ₂O ₇:Eu _0.006 ²⁺ was higher than the CRI of pc-LED coated with commercial red phosphor, due to the broad emission band of Rb ₂CaP ₂O ₇:Eu ²⁺ phosphor. In applying with three-band pc-LEDs, moreover, white pc-LED using Rb ₂CaP ₂O ₇:Eu ²⁺ phosphor had a higher CRI, than using commercial phosphor. These results indicated that Rb ₂CaP ₂O ₇:Eu ²⁺ phosphor could be a good candidate for a near-UV based w-LED.